Shepherdstown register. [volume] (Shepherdstown, Va. [W. Va.]) 1849-1955, 1887-09-02
About Lightning.

Every one is familiar with the fact
that lightning does not spring direct
from cloud 10 cloud or to the earth, but
pursues zigzag course. This is dueto
the fact that the air is not equally humid
throughout. Electricity always takes
the path which offers the least resistance
to its passage. Damp air is much bet
ter conducting medium than dry air
consequently the lightning selects the
damp air route, avoiding the drier strata
and zones II encounters, now directly,
now obliquely, until il reaches the oppo-
site cloud. where il subdivides into
number Of forks. Owing 10 the resist
ance which Il encounters In its path, in-
tense heat Is generated, which causes
the air to expand. Immediately after
the flash, the air again contracts with
great violence aud with loud report
which is echoed aud re- echoed among
the clouds. The report reaching the ear
of the listener from varying distances,
Is drawn out into series, and being
still further prolonged Sy the echoes,
the roll Of thunder is produced. lt tisa
curious fact that although the sound Of
thunder is exceedingly loud when heard
near at hand, the area over which II Is
audible is comparatively circumscribed.
The noise of a cannonade will be heard,
under favorable conditions, att distance
of nearly 100 miles, while the sound OF
thunder does not travel over fifteen
miles. The occurrence Of the thunder
and the lightning Is, OF course, slmulta'
neous; but as light travels faster than
sounJ-its passage is practically instan.
taneous-the fash may be seen several
seconds before the thunder Is heard.
The distance of thunder may thus be
approximately estimated. at Intervals oi
five seconds between the fash and the
thunder clap being allowed to each
mile.
Sheet lightning has the appearance OF
a sheet of flame momentarily illuminate
ing part OF the sky or cloud surface. it
Is, in reality. but the reflection Of light
ming flashing beyond the horizon or be-
hind the clouds, and at two great "A dis
tance for the thunder TO be audible.
But the most remarkable OF all the
manifestations of electricity Is globular
lightning, in appearance like ball of
fire moving leisurcly along, and remain
ing visible for several minutes. Many
curious accounts are related OF It's vag-
aries. One OF the most interesting and
circumstantial 10 that given by Mr.. Fitz-
gerald, county Donegal, Ireland, who
saw globe OF fire slowly descend from
the Glendowan mountains to the valleys
below. When IL first touched the ground
IL excavated hole about 20 feet square,
"as il il had been cut out with huge
knife" This was scarcely the work OF
a minute. For distance of 20 perchcs
IL ploughed trench about four feet
deep, aud, moving along the bank Of a
stream, it made furrow a foot In depth.
Finally II bore away part Of the bank,
five perches In length and hve.feet deep,
and "hurling the immense mass Into the
bed Of the stream Il. ilew to the opposite
peaty bank" The globe was visible
twenty minutes, and trayersed a dis
tance of a mile, showing that its prog
ress was, for lightning very slow indeed.
During the thunder storms of extreme
violence OIL Deeside, balls OF hre are oc-
casionally seen to roll down .he side OF
Locknagar. which are no doubt identical
with globular lightning.-Chamb0s
Journal.